Apparatus for the continuous production of curds

ABSTRACT

Apparatus for the continuous production of curds for use in cheese making, wherein renneted or acidified milk or mixture thereof is introduced under pulsation into a conduit whose wall is deformed under the effect of the pulsations and in which the curd is formed, and wherein the curd is collected at the outlet end of this conduit.

This is a division, of application Ser. No. 393,848, filed Sept. 4, 1973now U.S. Pat. No. 3,899,595.

This invention relates to apparatus for the continuous production ofcurds for making cheese.

The production of curds for making cheese traditionally involves asuccession of batch operations such as heating the milk to the rennetingtemperature, renneting, coagulation, slabbing the coagulum, more or lesspronounced syneresis of the curd and moulding thereof. This traditionalmethod is attended by various disadvantages, including dispersion of thephysico-chemical and bateriological characteristics of the variousbatches of curd obtained, and the difficulty of rationalising thevarious stages of production. Accordingly, these problems have to besolved by developing processes and apparatus which ensure continuity ofthe various manufacturing stages by circulating the treated product,whilst at the same time seeking to reproduce the chronology of theoperations and the physical and chemical parameters of the variousstages involved in the traditional manufacture of curds. Unfortunately,these processes come up against a serious difficulty due to the factthat the coagulum sticks to the walls of the coagulation chamber,generally tubular in shape, in which the product circulates. This isbecause the formation of aggregates adhering to the wall of thecoagulation chamber is an obstacle to the normal circulation of theproduct and can result in more or less pronounced blockage of thecoagulation unit. In addition, when these aggregates drop off the wallof the coagulation chamber, they form lumps of curd whosephysicochemical characteristics differ from those of the rest of theproduct and impair the homogeneity of the curd obtained.

The present invention seeks to obviate these disadvantages, and relatesto apparatus for the continuous product of curds by which it is possibleto obtain a curd of uniform quality without any blockage of thecoagulation unit. More particularly, the invention relates to apparatusfor the continuous production of cheese-grade curds from milk,distinguished by the fact that renneted and/or acidified milk isintroduced under pulsation into a conduit whose wall is deformed underthe effect of the pulsations and in which the curd is formed, and by thefact that the curd is collected at the output end of this conduit.

In the context of the invention, the term "milk" is intended todesignate a milk produced by female mammals, such as cows, she-goats,ewes or cow buffaloes. The milk constituting the starting productaccording to the invention can be either in its natural state or treatedby known methods. Thus, it can be subjected to filtration,pasteurisation and, if necessary, to regulation of its compositionbefore renneting and/or acidification.

The expression "renneted or acidified milk" means that one or moresubstances promoting the formation of a coagulum have been added to themilk. These substances, known among experts, are either enzymaticsystems, such as rennet, or acid substances or lactic ferments producinga certain degree of acidity in the milk. Although curdling of the milkcan be satisfactorily carried out by adding one or other of thesecoagulating agents, it is generally preferred in cheesemongery to userennet and lactic ferments in combination with one another. In theinterests of simplification milk with one or more of these coagulatingagents added to it will hereinafter be referred to as "renneted milk".

Although the invention is particularly well suited to the techniques ofproducing curd which are based on slow coagulation involving a greaterrisk of the coagulum sticking to the walls of the coagulation chamber,it has also proved to be of interest when the kinetics of coagulationare faster. It can be used for example when the milk is renneted coldand then heated.

In a first embodiment of the invention, the renneted milk is introducedinto the coagulation chamber under a pulsating effect, which producesappreciable variations in the rate of flow of the milk, by means of asuitable device such as a variable-output pump, for example a pistonpump, or a valve which is alternately opened and closed and whosethroughflow cross-section is periodically varied. The coagulationchamber is formed by a conduit in which the milk circulates duringcoagulation. The geometry of this conduit and the material of which itswalls are made are selected in such a way that this wall is deformedunder the influence of the pulsations applied to the milk. Thesepulsations produce elastic expansions and contractions in the wall whichare reflected in particular in slight localised variations in thethroughflow cross-section of this conduit. These variations in thethroughflow cross section counteract the phenomena which cause thecoagulum to adhere to the wall, and prevent blockage of the coagulationunit.

This conduit, whose throughflow cross-section is preferably circular,can be in the form of an optionally linear tube whose wall is made of amaterial with a relatively low modulus of elasticity, for example aplastics material such as polyvinyl chloride. The diameter of tube andthe thickness of its wall are selected in such a way that, by virtue ofthe mechanical characteristics of the material used, the wall is able toundergo local deformation under the effect of the pulsations applied tothe flow of renneted milk introduced into the tube.

The throughflow cross-section, the length and the general layout of theconduit (winding, bends, determining its loss of pressure) are of courseselected in such a way that the flow pattern of the product, moreparticularly its linear rate of flow at all points, is compatible withthe cohesion requirements of the coagulum formed, and in such a way thatthe residence time of the product in the conduit is sufficient to enablethe coagulum to be formed. On the other hand, the general layout of theconduit is preferably selected in such a way that the milk circulatingin the conduit follows an ascending course.

The renneted milk introduced into the coagulation conduit can beprepared either by heating to the so-called renneting temperature, whichis of the order of 25° to 40°C, followed by renneting (addition ofrennet and/or lactic ferments), or by cold renneting followed byheating. Since these various methods of treating the milk have anappreciable influence upon the kinetics of coagulation, it is advisableto adapt the geometric characteristics of the conduit to these kinetics,in particular the length of this conduit which, for a given rate ofsupply, determines the residence time of the product in the coagulationunit.

The rate at which the milk is introduced into the coagulation unit andthe form of pulsation applied to the flow of milk should be selected independence both upon the kinetics of coagulation and upon the geometricand mechanical characteristics of the conduit so as to obtain localdeformation of the conduit without at the same time adversely affectingthe cohesion of the coagulum formed. The pressure under which the milkis introduced into the coagulation unit should of course be above aminimum value so that it is possible to overcome the loss of pressureintroduced by the conduit and the hydrostatic pressure generated ifnecessary by the difference in level between the inlet end and theoutlet end of this conduit.

The coagulum formed is collected at the outlet end of the coagulationconduit by an arrangement which allows draining and then moulding, ormoulding and then draining.

In a modification of the first embodiment of the invention, additionaldeformation can be produced in the coagulation conduit by applyingmechanical forces to it, for example by using a helically wound conduitand by locally modifying the winding diameter through the application ofradial pressures to the conduit.

It is of course possible to arrange several coagulation units parallelto one another downstream of the systems delivering the milk underpulsation, the performances of these systems being selected independence upon the number of coagulation units and their geometriccharacteristics.

As described above, the coagulum formed is generally fragmented onleaving the coagulation conduit under the effect of its own weight, forexample when it is collected on a draining screen. A number ofdifferently sized particles or lumps is formed under these conditions,their distribution being fairly heterogeneous so that they offer afairly large syneresis surface. A coagulum of this kind is thusparticularly suitable for rapid draining and, after draining, forms acurd whose mineral substance, especially calcium, content is relativelyhigh. A curd of this kind, generally referred to in cheesemongery as a"rennet-like curd" can be used with advantage for the manufacture ofsuch cheeses as Pont-l'Eveque or Reblochon.

However, it can be of advantage, for example in the manufacture of suchcheeses as camembert or brie, to obtain a curd whose mineral substancecontent, and especially its calcium content, is considerably lower. Acurd of this kind, known in cheesemongery as a "lactic curd", isgenerally obtained by slow draining which leaves the calcium enough timeto react with the lactic acid to form lactates which are eliminatedduring draining.

It can also be of interest to obtain by controlled draining curds of anintermediate type semi-rennet/semi-lactic in character which aresuitable for the production of such cheeses as Carre de l'Est orCoulommiers.

In a second embodiment of the invention, it is possible continuously toobtain a curd whose degree of fragmentation, which determines thedraining rate and, hence, the mineral substance content of the curd, canbe adjusted as required. This second embodiment of the invention isdistinguished by the fact that the coagulable protein content of themilk is increased, after which the milk is introduced under pulsation,after renneting or acidification or both, into the conduit having a wallwhich can be deformed under the effect of the pulsations.

In the context of the invention, the expression "coagulable proteins" isintended to designate the proteins, such as casein in its native ornon-degraded state, which are able to coagulate under the effect of anenzyme or an enzymatic system responsible for coagulation of the milk,such as rennet, or under the effect of acidification, optionallycombined with an enzymatic action. Accordingly, this definition does notinclude serum proteins (such as lactalbumin) which coagulate under theeffect of heat, but are not coagulated either by rennet or byacidification. However, the expression "the coagulable protein contentof a milk is increased" by no means excludes the possibility ofincreasing the content in the milk both of coagulable proteins such ashave just been described, and such proteins as serum proteins.

It has been found that the cohesion characteristics of the curd formedin the coagulation conduit, i.e. the ability of this curd to withstanduncontrolled fragmentation, occurring for example spontaneously at theoutlet end of the coagulation conduit under the weight of the curditself, is greatly influenced by the coagulable protein content of thetreated milk. This resistance to uncontrolled fragmentation increaseswhen the coagulable protein content of the treated milk increases.Accordingly, it is possible, by adjusting the coagulable protein contentof the milk to a suitable value, to collect a coagulum with improvedcohesion, which can be more or less pronounced according torequirements, at the outlet end of the coagulation conduit. Ifnecessary, a coagulum of this kind can be subsequently fragmented, forexample by slabbing, into pieces of suitable size offering a syneresissurface such that draining takes place at the required rate to give acurd with a suitable mineral substance content after draining.

If, on the other hand, the coagulable protein content of the milk isadjusted to high values, corresponding for example to totalconcentrations of non-fat solids of the order of 25 to 30 %, it ispossible to collect at the outlet end of the coagulation conduit acoagulum of extremely firm consistency which can be cut into unitaryslabs corresponding in volume to the required volume of coagulum toobtain, after draining, a unitary cheese. This modification has provedto be of particular interest in the manufacture of cheeses intended tobe sold "by the piece", because it enables unitary slabs of curd to beobtained whose weights show greatly reduced dispersion.

This embodiment of the invention also has other advantages, including animprovement in the hourly output of the coagulating machine, which isdirectly related to the increase in coagulable material content, andsimplification of the draining operations because draining can becarried out directly in the moulds by virtue of the relative reductionin the quantity of serum to be eliminated, whilst at the same timecontrolling the draining rate.

The coagulable protein content of the milk can be increased either byadding a suitable quantity of coagulable proteins to the milk or bytreating the milk by a selective filtration process, such asultrafiltration.

Coagulable proteins can be added to the milk in the form of an aqueoussolution of these proteins in their native or non-degraded state inwhich the concentration of these proteins is higher than in the milk. Anaqueous solution of this kind can be obtained by subjecting milk toultrafiltration or by filtering on gel a milk of which the first elutionfraction is collected. It is also possible to add to the milk a driedproduct, for example in powder form obtained from an aqueous solution ofthese proteins by drying under such conditions that the coagulableproteins do not undergo any appreciable changes modifying theirbehaviour with respect to the coagulating agents.

Irrespective of whether it is in the form of an aqueous solution or inthe form of a dry product, the coagulable protein concentrate cancontain other substances than the coagulable proteins, for example serumproteins. For example, an aqueous solution rich in proteins obtained byultrafiltration of a skimmed milk is particularly suitable for carryingout the process. A solution such as this can contain for example 18.2 %by weight of coagulable proteins and 6.1 % by weight of serum proteinsfor a total non-fat solids content of 30 % (the other substances presentin this solution being essentially lactose and mineral salts). Thissolution added in a suitable quantity to the treated milk enables thecoagulable protein content to be adjusted to the required value.

If, on the other hand, the coagulable protein concentration of the milkto be treated is increased by subjecting the milk to ultrafiltration,the serum protein content of the milk is increased correlatively inproportions governed by the characteristics of the semi-permeablemembrane (s) used.

Such an increase in the serum protein content can prove to be ofadvantage because it enables a curd to be obtained whose protein contentis greater than that of a curd obtained from an equivalent quantity ofmilk by conventional means. This is also true if the milk has beenenriched in proteins by the addition of a protein concentrate containingserum proteins, the comparison having to be made in this case inrelation to a curd obtained by a traditional process from the totalquantity of milk used, including the quantity of milk used to preparethe protein concentrate.

In one particularly advantageous modification of the second embodimentof the invention, a milk is subjected to an ultrafiltration treatment toincrease its coagulable protein content. This treatment comprisesseparating the milk, by filtration through one or more semi-permeablemembranes, into two liquid fractions differing in their chemicalcomposition, and collecting the fraction retained by the semi-permeablemembrane, the retained fraction having an appreciably increased proteincontent. The other fraction, known generally as the "permeate", is anaqueous solution containing substances of relatively low molecularweight, such as lactose and mineral salts, together with certainnitrogen-containing substances. If necessary, the fraction collected canalso be subjected to one or more additional ultrafiltration treatmentsso that it has the required chemical composition. Although theultrafiltration treatment can be carried out effectively with wholemilk, it is generally preferred to use skimmed milk to eliminate theneed for frequent cleaning of the semi-permeable membranes.

Ultrafiltration can be carried out by means of a membrane whosepermeability is such that the low molecular weight constituents of themilk (lactose, mineral salts, non-protein nitrogen-containingsubstances) are able to pass through it whilst the constitutents ofhigher molecular weight, notably the coagulable proteins such as casein,are retained. It is possible for this purpose to use standardcommercially available membranes, for example those which have beenproposed for separating proteins from whey by ultrafiltration. Membranesof this kind can be made of cellulose acetate or synthetic polymers suchas polyvinyl chloride or polyacrylonitrile.

The ultrafiltration installation can comprise porous tubes whoseinternal or external surface is covered by the semipermeable membraneand which are arranged in bundles, or can be formed by porous plateseach supporting a semi-permeable membrane and arranged in adjacentframes leaving a suitable interval between the plates. These varioustypes of ultrafiltration systems are also available on the chemicalindustry market.

The milk is brought into contact with the semi-permeable membrane underpressure and preferably in a state of turbulence so as to avoid thepolarisation phenomena which adversely affect the output of theoperation. The temperature of the milk during ultrafiltration is not acritical parameter providing it remains compatible with the viscosityrequirements of the milk and does not in any way impair the integrity ofthe product treated and of the membranes. This temperature can beadjusted to a value of from 2°C to 70°C, although in the interests ofsimplification it is generally preferred to carry out ultrafiltration atambient temperature.

The ultrafiltration treatment is repeated as often as is necessry,depending upon the composition of the product it is desired to obtain,either by arranging an adequate number of membranes in the path followedby the milk or by recycling the milk into the ultrafiltration apparatus.The composition of the liquid product retained, in particular its solidscontent, is selected in dependence upon the cohesion characteristics ofthe curd which it is desired to obtain, and upon the type of cheeserequired. In the case of skimmed milk treated by ultrafiltration, thesolids content can reach values of from 10 to 30 % by weight.

If the liquid product has been prepared by ultrafiltration of skimmedmilk, a suitable quantity of edible fats is if necessary added to theskimmed milk. These facts can be either of animal origin (for examplecream of milk or oil of butter), or vegetable origin (for example peanutoil). The required quantity of fat is selected in dependence upon thetype of cheese required. For example, it can be of the order of 45 to 50% of the weight of the total solids which will be retained in thecheese.

The liquid product, which in the interests of simplification is referredto hereinafter as "ultrafiltered milk", is then heated to the so-calledcoagulation temperature, which is of the order of 25° to 50°C, followedby the addition of rennet or suitable lactic ferment or mixture thereofselected according to the type of cheese required. Ferments of this kindare well known among experts so that there is no need to describe themin detail here. The addition of rennet or lactic ferments on mixturethereof can of course be carried out continuously by means of meteringpumps which introduce these ingredients into the circulatingultrafiltered milk before it enters the actual coagulation conduit. Inanother modification, the ultrafiltered milk accommodated in a storagetank is inoculated with suitable lactic ferments and then left standingto incubate for a period long enough to ensure that the lactic fermentsdevelop a certain acidity, this period being itself governed by theincubation temperature. When the required pH-value (for example 6.2 forcheese of the camembert type) is reached, the inoculated, ultrafilteredmilk is heated to the coagulation temperature, renneted by means of ametering pump as it circulates towards the coagulation conduit andintroduced under pulsation into the coagulation conduit.

It is pointed out that the pH-value of the ultrafiltered milk at therenneting stage and its subsequent development have a considerableinfluence upon the consistency and structure of the curd obtained at theoutlet end of the coagulation conduit. For this reason, it is advisablein each case to determine the optimum pH range, especially duringrenneting and introduction of the ultrafiltered milk into thecoagulation chamber, and the coagulation time which determines thecondition of the curd at the outlet end of the coagulation chamber, soas to obtain a curd with the required firmness and cohesion.

It has been found that certain characteristics of the curd obtained areclosely associated with the non-fat solids content of the ultrafilteredmilk. Thus, if the non-fat solids content of this ultrafiltered milk isgreater than 15 % by weight, the curd will not readily reintegrate, inother words if this curd is fragmented it will be difficult to obtain ahomogeneous curd mass from several fragments. By contrast, if thenon-fat solids content of the ultrafiltered milk is less than 15 % byweight, it is possible to cut the curd into slabs of suitable size andto reconstitute a homogeneous curd mass from these slabs by introducingthem for example into a draining mould in which they spontaneouslyreintegrate.

These differences in behaviour of the curd arising out of the non-fatsolids content of the ultrafiltered milk enable the second embodiment ofthe invention to be divided into two principal modifications.

The first modification comprises using an ultrafiltered milk whosenon-fat solids content is less than 15 % by weight. After renneting, theultrafiltered milk is introduced under pulsation into the coagulationconduit. The coagulum formed, whose firmness is more pronounced, thehigher the non-fat solids content of the ultrafiltered milk, is obtainedat the outlet end of the coagulation conduit in the form of a continuouscylinder which is cut into slabs of suitable size selected in dependenceupon the draining rate which it is desired to obtain. These slabs arecollected on a moulding and draining arrangement, such as drainingmoulds in which the slabs of curd drain and reintegrate to form ahomogeneous curd mass corresponding to a cheese.

The second modification comprises using an ultrafiltered milk whosenon-fat solids content is greater than 15 % by weight. Thisultrafiltered, renneted milk is introduced under pulsation into thecoagulation conduit. The coagulum formed is obtained at the outlet endof the coagulation conduit in the form of a continuous cylinder. Thiscontinuous cylinder is cut into unitary slabs, whose weight correspondssubstantially to that of the required cheese, and not into slabs of moreor less large dimensions. Thus, to produce cheese of the camembert typefor example, the coagulation conduit used is circular in shape with adiameter of approximately 100 mm, and slabs of constant thickness arecut, for example by means of a wire cutter adapted to the rate ofadvance of the cylinder emerging from the coagulation conduit, whoseterminal section is vertically arranged.

The slabs cut, whose consistency and firmness are such that they areeasy to handle, can be separated and collected in suitable moulds whosedimensions are preferably slightly greater than those of the cut slabs.The slabs of coagulum arranged in the moulds are slowly deformed tofollow the geometry of the moulds and each form a cheese ofpredetermined weight. In one modification, which can be used when thecoagulation conduit has a vertical terminal section, the coagulum is cutwithout separation of the slabs and, continuing its vertical progressionin the form of a stack of unitary slabs, enters a second verticalchamber of identical cross section. This second chamber can then be usedas a unit for storing and transporting an assembly of unitary slabs ofcurd.

So far as this second modification is concerned, it is pointed out thatit is preferred to use an ultrafiltered milk whose non-fat solidscontent is greater than 20 % by weight. The reason for this is that, fora non-fat solids content of this order, the quantity of serum to beremoved by draining is small so that there is no need to slab the curdto eliminate this serum.

If, by contrast, an ultrafiltered milk with a non-fat solids content offrom 15 to 20 % by weight is used, the quantity of serum to be removedgenerally necessitates fragmentation of the coagulum. This fragmentedcoagulum, which is not able to reintegrate, cannot be used for reforminga homogeneous curd mass. However, it is possible to use ultrafilteredmilk with a non-fat solids content of from 15 to 20 % by weight in themanufacture of cheese in divided form, such as cottage cheese.

The curd obtained by one or other of these modifications then undergoesthe usual operations required to produce the required cheese, such asacidification, salting and ripening.

The invention also relates to an apparatus and comprises at least onecoagulation unit in the form of a conduit, in which the coagulum isformed, and means for introducing and circulating the renneted oracidified or renneted and acidified milk in this conduit, and isdistinguished in particular by the fact that it comprises means forapplying pulsation to the flow of milk entering the conduit, and by thefact that the wall of this conduit is capable of deforming under theeffect of these pulsations.

The coagulation conduit is preferably in the form of a circular tubewhose constituent material is a material with a low modulus ofelasticity which is capable of undergoing elastic deformation under theeffect of relatively weak stresses, such as a polyvinyl or polyethylenepolymer for example. Although this coagulation conduit can be arrangedin a straight line, it is preferred to wind it helically to save space.

The milk can be introduced into and circulated in the coagulationconduit by means of any suitable device, such as a centrifugal pump orthe like, or simply by the application of pressure.

The pulsating effect applied to the flow of milk can be obtained bymeans of numerous types of devices such as pulsating pumps, for examplepiston pumps which not only circulate the milk, but also pulsate it inthe required manner. It is also possible to use, in combination with acirculating means (pump or pressurisation), a valve which can bealternately opened and closed or whose throughflow cross-section can beperiodically varied, for example a pneumatically or electricallycontrolled valve.

Several embodiments of the apparatus according to the invention areillustrated by way of example in the accompanying drawings, wherein:

FIG. 1 diagrammatically illustrates a first embodiment of the invention.

FIG. 2 is a plan view of the coagulation unit shown in FIG. 1.

FIG. 3 is a curve showing the variation, as a function of time, in theoutput per second of product obtained at the outlet end of thecoagulation unit shown in FIG. 1.

FIG. 4 diagrammatically illustrates a second embodiment of theinvention.

FIG. 5 is a partial view of an installation constituting a modificationof the installation illustrated in FIG. 4.

As shown in FIG. 1, the installation comprises the following componentsconnected in series in the order listed by a pipeline 11: a storage tank1 equipped with a stirrer 2 and a device for keeping it at a constanttemperature (not shown), a constant-level chamber 3, a centrifugal pump4, a plate heater 5, a centrifugal pump 6, a pneumatically controlledvalve 7, a variable-opening valve 8, and a coagulation unit 9 in theform of a helically wound tube 10 of polyvinyl chloride. This tube 10,which has a diameter of 100 mm, a thickness of 2 mm and a length of 20m, is arranged in an octagonal frame 12. This frame is subjected to theaction of pneumatic jacks 13 (shown in FIG. 2) and is capable ofdeforming to such an extent that the radius of curvature of the helicaltube 10 is modified by about 30 %.

The installation also comprises two pipelines 14 and 15 connected inparallel to that section of the pipeline 11 situated between the heater5 and the pump 6. By means of the pipelines 14 and 15 equipped withmetering pumps 16 and 17, respectively, it is possible to introduce thequantities of lactic ferment and rennet required to obtain the type ofcheese desired. These additives are intimately mixed with the milk bythe centrifugal pump 6.

Finally, the installation comprises a drainage screen 18 in the form ofa moving belt which is permeable to liquids. A perforated hopper 19,whose cross-section is several times greater than that of the requiredcheese, is arranged beneath the screen 18 to collect the drained curd.

The installation shown in FIG. 4 comprises a certain number ofcomponents arranged in series and connected by a pipeline 21. Thesecomponents, listed in the order in which they are arranged in thedownstream direction, are the following:

- a storage tank 22 for the ultrafiltered milk equipped with a stirrer23 and a device for keeping it a constant temperature (not shown),

- a centrifugal pump 24,

- a plate heater 25,

- a centrifugal pump 26,

- a pneumatically controlled valve 27,

- a variable-opening valve 28,

- a coagulation unit in the form of a polyvinyl chloride tube 29 woundhelically on a metal frame 30,

- a slabber 31 in the form of a blade or stretched wire displacedvertically by a pneumatic jack (not shown),

- a receptacle 32 in the form of a perforated hopper or a mould whoseperforated wall allows the serum to flow out.

This installation comprises a pipeline 33 equipped with avariable-output pump 34 and connected to the pipeline 21 between thetank 22 and the centrifugal pump 24. This pipeline 33 enables therequired quantity of fats to be continuously added to the ultrafilteredmilk. The installation also comprises two pipelines 35 and 36 connectedin parallel to the pipeline 21 between the heater 25 and the centrifugalpump 26. These pipelines 35 and 36, equipped with metering pumps 37 and38, respectively, enable the required quantities of lactic ferment andrennet to be continuously introduced.

FIG. 5 is a view of the coagulation and slabbing unit of one modifiedembodiment of the installation. This modified embodiment is particularlysuitable for use with ultrafiltered milk whose non-fat solids content isrelatively high, for example of the order of 20 to 30 % by weight.

The first section of an installation of this kind, i.e. the componentssituated upstream of the coagulation unit which are not shown in FIG. 5,is similar to that illustrated in FIG. 4.

The coagulation unit is in the form of a polyvinyl chloride tube 39wound helically on a metal frame 40. The upper part of the tube 39 iswound around the frame 40 with a higher pitch, and terminates in avertical section 41 so that the curvature of this upper section is notmore pronounced than that of the lower spirals so as not to interferewith the advance of the coagulum through the tube.

The installation also comprises a cutting unit with a cutter 42displaced horizontally by a pneumatic jack 43 equipped with a returnspring 44. This pneumatic jack is connected through a pipe 45 equippedwith an electric valve 46 to a source 47 of compressed air. The electricvalve 46 is regulated by an electric control device 48 which is itselfconnected to a photoelectric cell 49. This photoelectric cell isarranged at a predetermined height d above the outlet end of the tube 39in relation to a light source 50 emitting a light beam directedhorizontally towards the cell 49. When the cylinder of curd emerges fromthe tube 39 at the height d, it interrupts the light beam so that thephotoelectric cell transmits a signal which, through the electriccontrol device 48, closes or opens the electric valve 46 and operatesthe cutter 42. The following signal operates the cutter in the oppositedirection. Accordingly, it is possible by this arrangement to cutunitary slabs of curd of constant thickness.

The following examples illustrate the invention, although it is by nomeans confined to the conditions described therein.

EXAMPLE 1

A milk containing 34 g/l of fats, stored at 10°C in the tank 1, isheated to 35°through circulation in the plate heater 5. 1 % by volume ofa ferment consisting of an association of Streptococcus lactis,Streptococcus cremoris, Streptococcus citrovorus and Streptococcusdiacetilactis, and 0.03 % by volume of a rennet with a strength of1/10,000, are then introduced into the milk circulating in the pipeline11 by means of the metering pumps 14 and 15. The lactic ferment and therennet are intimately mixed with the milk by the centrifugal pump 6whose output is at least twice the total output of the installation. Thepneumatically controlled valve 7 is operated by an automatic devicewhich closes it for 1 second and then opens it for 1 second inrepetitive fashion. This operation of the valve produces a pulsatingeffect upon the flow of milk which in turn produces deformation of thecoagulation conduit 10 reflected in local variations in the diameter ofthe conduit of the order of 0.15 %. The opening of the valve 8 isregulated to adjust the rate of flow to 940 liters per hour, whichcorresponds to an average linear rate of flow of the milk duringcoagulation in the tube 10 of the order of 2 meters per minute, and to aresidence time of the product in the coagulation unit of the order of 10minutes.

The pulsating effect produced by opening and closing the valve 7, whichis reflected in a periodic variation in the output of product at theoutlet end of the coagulation unit, is illustrated in FIG. 3.

On the other hand, pressures are periodically applied to the frame 12 bymeans of the jacks 13, thus modifying the radius of curvature of thehelical conduit by about 30 %.

The curd collected at the outlet end of the conduit 10 is distributedonto the drainage screen 18 whose drainage rate is regulated to 2 metersper minute. The drained curd then drops into the hopper 19 where it isavailable for moulding and the subsequent operations involved in themanufacture of cheese.

EXAMPLE 2

This Example, illustrates the use of in the installation shown in FIG.4.

2000 liters of a skimmed milk containing 9 % by weight of non-fat solidsare subjected to an ultrafiltration treatment to obtain 947 liters of anultrafiltered milk containing 13 % by weight of non-fat solids.

The ultrafiltration treatment is carried out in an apparatus comprising,in series, 10 sub-assemblies, each sub-assembly being formed by 5 porousplates arranged parallel to one another and supporting on their twosurfaces a semi-permeable membrane with a surface area of about 0.1 m².This ultrafiltration system is manufactured by Societe Rhone. Poulenc(Paris), and the membranes, which have a total surface area of 10 m²,bear the name "type Iris 3069". The skimmed milk is introduced into theultrafiltration arrangement at a rate of 6000 liters per hour, whichmakes it possible to establish suitable turbulence conditions, and isrecycled in this arrangement for 13 hours by way of a buffer tank. The947 liters of ultrafiltered milk collected in the buffer tank aretransferred to the tank 22 where they are stored at 20°C. Theultrafiltered milk has the following composition:

lactose 5.0 %

mineral salts 0.7 %

casein 5.75 %

soluble proteins 1.55 %

The ultrafiltered milk is then introduced at a rate of 300 liters perhour into the conduit 21 where cream of milk containing 60 % of fats isadded to it continuously at a rate of 28 liters per hour through thepipeline 33 by means of the pump 34.

The ultrafiltered milk with the fats added to it is then transported bymeans of the pump 24 and enters the heater 25 in which it is heated to35°C. 1% by volume of a ferment consisting of an association ofstreptococcus lactis, Streptococcus cremoris, Leuconostoc citrovorum andStreptococcus diacetylactis, and 66 cm³ /h of a rennet of strength1/10,000, are then introduced into the heated, ultrafiltered milk bymeans of the metering pumps 37 and 38. The lactic ferment and the rennetare intimately mixed with the ultrafiltered milk by the pump 26.

The pneumatically controlled valve 27 is operated by means of anautomatic device which opens it for 0.5 seconds and then closes it for0.5 seconds in a repetitive manner. This repeated opening and closing ofthe valve produces a pulsating effect in the flow of ultrafiltered milkwhich in turn produces deformations in the coagulation tube 29 which hasan internal diameter of 80 mm, a thickness of 1.5 mm and a length of 22m. The opening of the valve 28 is regulated to adjust the rate of flowof product through the coagulation tube to 334 l/h, which corresponds toan average linear velocity of the product of the order of 1.1 meter perminute, and to a residence time of the product in the coagulation unitof around 20 minutes.

The curd collected at the outlet end of the conduit 29 is in the form ofa homogeneous cylinder which is fragmented by the cutter 31 intoapproximately 15 cc. pieces which are collected in drainage mouldsarranged on a turntable. The curd deposited into these moulds drains andreintegrates. It is then subjected to the conventional operationsinvolved in the manufacture of cheese.

EXAMPLE 3

1000 liters of a skimmed milk containing 9 % of non-fat solids aresubjected to an ultrafiltration treatment to obtain 185 liters of anultrafiltered milk with a non-fat solids content of 25.5 % by weight.

This ultrafiltration treatment is carried out in the apparatus describedin Example 2. The skimmed milk is introduced into the ultrafiltrationapparatus at a rate of 6000 liters per hour and is recycled in thisapparatus for 10 hours by way of a buffer tank. The 185 liters ofultrafiltered milk collected are transferred to the tank 22 where theyare stored at 20°C. The ultrafiltered milk has the followingcomposition:

lactose 5.0 %

mineral salts 0.7 %

casein 15.6 %

soluble proteins 4.2 %

The milk is introduced at a rate of 100 liters per hour into thepipeline 21 where cream of milk with a 60 % fat content is added to itcontinuously at a rate of 30 liters per hour through the pipeline 33 bymeans of the pump 34.

The ultrafiltered milk then enters the heater 25 where it is heated to atemperature of 35°C. 2 % by volume of the lactic ferment described inExample 2 and 26 cc/h of a rennet of strength 1/10,000, are thencontinuously introduced into the ultrafiltered milk by means of themetering pumps 37 and 38. The pneumatically controlled valve 27 isoperated in the same way as described in Example 2 to produce apulsating effect in the flow of ultrafiltered milk. The average rate offlow of the ultrafiltered milk is adjusted to 132 liters per hour bymeans of the valve 28.

The coagulation and cutting untis used in this Example are shown in FIG.5. The coagulation unit is in the form of a coagulation tube 39 ofpolyvinyl chloride with an internal diameter of 80 mm, a thickness of1.5 mm and a length of 6.5 m. The product circulates in the coagulationtube at an average linear velocity of 44 cm per minute, whichcorresponds to a residence time of the product in the coagulation unitof 15 minutes.

The curd emerging at the outlet end of the vertical section 41 of thetube 39 is in the form of a firm, homogeneous cylinder which is cut intounitary slabs 30 mm thick by means of the cutter 42 controlled by thephotoelectric cell 49.

These unitary slabs are removed and deposited into moulds whose diameteris slightly greater than theirs and subsequently undergo theconventional operations involved in the manufacture of cheese.

I claim:
 1. An apparatus for the continuous production of curds for usein cheese making, comprising at least one coagulation unit in the formof a conduit in which the coagulum is formed, means for introducing andcirculating renneted milk in this conduit, the term "renneted milk"indicating herein milk to which has been added one or more substancespromoting the formation of a coagulum, such substances includingenzymatic systems of which rennet is an example, acid substances andlactic ferments, and means for applying a pulsating effect to the flowof milk introduced into the conduit, and wherein the wall of thisconduit is capable of being deformed under the effect of thesepulsations.
 2. An apparatus as claimed in claim 1, wherein the meansapplying pulsations to the flow of milk entering the conduit alsocirculate the milk.
 3. An apparatus as claimed in claim 2, wherein theaforementioned means are in the form of at least one pulsating pump. 4.An apparatus as claimed in claim 1, wherein the means applying thepulsating effect to the flow of milk entering the conduit consist of atleast one valve positioned in the path followed by the milk circulatingupstream of the aforementioned conduit.
 5. An apparatus as claimed inclaim 4, further comprising automatic control means for controlling saidvalve.
 6. An apparatus as claimed in claim 5, further comprising anautomatic device adapted for periodically opening and closing saidvalve.
 7. An apparatus as claimed in claim 1, wherein the conduit is inthe form of a tube made of a material with a low modulus of elasticity.8. The apparatus as claimed in claim 1, further comprising a frame aboutsaid conduit, said conduit being in the form of a helically wound tubeaccommodated in said frame.
 9. An apparatus as claimed in claim 8,further comprising means for applying external mechanical forces to saidconduit in order to deform it, and wherein the means for applying themechanical forces are adapted to cooperate with said frame to modify thewinding diameter of the conduit.
 10. An apparatus as claimed in claim 1,wherein said apparatus comprises means for applying external mechanicalforces to the conduit in order to deform it.
 11. An apparatus as claimedin claim 1, wherein said conduit has a vertical terminal section with anupper edge, and said apparatus further comprises a cutting unitpositioned above said upper edge of said conduit for acting in asubstantially horizontal plane.